<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      const hobby = new Set();
      hobby.add("css");
      hobby.add("html");
      hobby.add("js");
      hobby.add("vs");
      // hobby.delete("js");
      hobby.clear();
      console.log('has("js")', hobby.has("js"));
      console.log("size", hobby.size);
    </script>
  </body>
</html>
